Chest radiography represents the widest used modality in medical imaging because of its high applicability to a multitude of medical problems. However, as now practiced multiple studies have shown that intervening structures and insufficient contrast result in a disturbingly high percentage of missed lesions. Further, many studies require multiple tomograms with their associated increased dose and image artifacts for adequate characterization of lesions. Recent progress by our group in energy-selective digital radiography (EDR) shows great promise in overcoming these problems. By using the information present in the x-ray energy spectrum, the technique has the capability of producing separate images of bone and soft tissue which dramatically improve the visualization of structures in the thorax. Furthermore, the information is extracted based on physically rigorous techniques developed by our group for computed tomography. Our results indicate that it is sufficiently accurate for in-vivo tissue characterization. Using our unique experimental facilities consisting of a modified General Electric 8800 CT scanner with a high speed voltage switching x-ray generator, we have experimentally shown the capabilities of our techniques. We propose to upgrade our clinical system and to carry out clinical trials to rigorously prove our hypothesis that ESDR provides significant improvement over conventional chest radiography in the detection and characterization of chest lesions, especially those obscurred by overlying bone. Given the success of the initial clinical studies and the extensive analytical and experimental efforts that have been made, this system is in an ideal position to initiate rigorous clinical studies. In parallel with the clinical evaluation, we propose a program of engineering improvements which will make the performance of the bone-subtracted chest image comparable to or greater than that of chest tomography. The initial results of these improved techniques appears to be very promising.